I think there's another thread about this somewhere on this site...

But anyway, I would think that if you're just starting out, you wouldn't want to have a lot of forums. Otherwise, they're going to be empty untli you attract a lot of users to fill them up. Once you've got a good user base you can start to split them up.

For example, if you have a "graphics" forum, and you get people posting in there, after a while you can split it up into "graphics", "graphics requests", "graphics showcase", etc.